Distillation of cyclohexanone from mixtures containing cyclohexanone, cyclohexanol, and water



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DISTILLATION OF CYCLOHEXANONE FYROM MIXTURES GONTAINING CYCLOHEXANONE,CYCLOHEXANOL, AND WATER Filed March 12, 1956 MN m INVEN-roR ROBERT I.WILLISTON ATTORNEY United States Patent O DISTILLATION OF CYCLOHEXANONEFROM MIXTURES CONTAINWG CYCLOHEXA- NONE, CYCLOHEXANOL, AND WATERApplication March 12, 1956, Serial No. 570,891

4 Claims. (Cl. 202-42) The invention relates to cyclohexanone and moreparticularly refers to a new and improved process for continuouslyseparating cyclohexanone from mixtures containing it together with waterand cyclohexanol to obtain a cyclohexanone product of high purity.

Cyclohexanone is commercially produced by vapor phase dehydrogenation ofcyclohexanol at elevated temperatures over a Zinc-copper catalyst. Thecrude product thus obtained usually contains over 90% of cyclohexanoneand less than about 10% of impurities, notably cyclohexanol and water,as well as small amounts of phenol and by-product hydrocarbons such ascyclohexene,

Under ordinary pressure cyclohexanone and cyclohexanol boil within 5 ofeach other (155 C. and 160 C. respectively), and hence cannot be readilyseparated by distillation. However, under reduced pressures of less than100 mm. Hg abs. these compounds possess sufficiently differentvolatilities, i. e. more widely diiferent boi-ling points such as topermit fractional distillation. Water, as a component of the mixtures ofcyclohexanone and cyclohexanol, complicates the situation in that waterforms azeotropes with both cyclohexanone and cyclohexanol, which possessvery close boiling points (96 C. and 98 C. respectively, at 760 mm. Hgabs). Consequently, in view of the small difference in boiling points ofthese azeotropes, these substances cannot be readily separated bydistillation as long as water is present in mixture therewith and it isnecessary to remove water from the mixture prior to separation of thecyclohexanone in order to prevent contamination of the cyclohexanonewith cyclohexanol.

Crude, wet cyclohexanone containing cyclohexanol and small amounts ofother impurities may be distilled in a batch operation by first removinga forerun -containing the water, hydrocarbon and other impurities whichare separately collected and then fractionally distilling the residue invacuo to separate the cyclohexanone. While the batch distillation issatisfactory for the separation of small amounts of cyclohexanone, forlarge volume operations, a continuous distillation process is moredesirable and economical.

A continuous distillation process for purifying crude cyclohexanone hasbeen suggested wherein a stream of crude cyclohexanone is introducedinto a fractionating column, the water removed as overhead in the formof cyclohexanone-water and cyclohexanol-water azeotropes, whiledehydrated, crude cyclohexanone is removed as bottoms. The overhead iscondensed and stratied into two layers: The upper layer poor in water isreturned to the iirst column, while the lower layer rich in water isintroduced into a second column for removal `of water. This involves theuse of two continuous fractionation columns with their attendantaccessories and requires recycling two wet fractions to the rst columnwith increased formation of auto-condensation products due to longresidence time. The dry, crude cyclohexanone from the rst column isfractionated in a third column to remove cyclohexanol and other highboiling impurities.

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An object of the present invention is to provide a continuous processfor separating cyclohexanone in high yield and purify from crude, wetcyclohexanone containing cyclohexanol. Another object of theinvention'is to provide a continuous distillation process for purifyingand separating cyclohexanone from crude, wet cyclohexanone containingcyclohexanol which is eicient in operation and economical inconstruction. Other objects and advantages will be apparent from thefollowing description and accompanying drawing.

In accordance with the process of the present invention cyclohexanone inhigh yield and purity may be separated yfrom crude, wet -cyclohexanonecontaining cyclohexanol in a continuous operation by continuouslyfeeding a stream of crude, wet cyclohexanone into a fractionatingcolumn, continuously introducing cyclohexene into said fractionatingcolumn, continuously removing as vapor from the top of the fractionatingcolumn as azeotrope composed of water and cyclohexene, continuouslycondensing said vapor azeotrope, continuously separating said condensateinto an aqueous phase and an oil phase containing cyclohexene, returningcyclohexene from the oil phase to the fractionating column, continuouslywithdrawing dehydrated cyclohexanone containing cyclohexanol from thebottom of the fractionating column, continuously passing said dehydratedcyclohexanone-cyclohexanol to a second fractionating column maintainedat an absolute pressure below mm. Hg, continuously removingcyclohexanone vapor of high purity from the top of said secondfractionating column, continuously condensing and collectingV said purecyclohexanone and continuously withdrawing cyclohexanol as bottoms fromthe bottom of the second fractionating column.

Referring to the drawing, the feed to the continuous distillation systementering through line 1 is crude, wet cyclohexanone which may beproduced 'by dehydrogenation of cyclohexanol and is a mixture of 80-90%or more of cyclohexanone, usuallyy about 5-'l0% cyclohexanol and about0.5-3% water together with small amounts of other impurities such lasphenols, polymers and hydrocarbons. I-n crude cyclohexanone produced by'hydrogenation of phenol followed by dehydrogenation of resultantcyclohexanol the resultant crude pro-duct contains about 1-2%cyclohexene as an impurity. Fractionating column 2, into which feedenters through line 1, may be any suitable fractionat-ing tower,preferably a column of the bubble cap type. Heat is provided in thebottom of fractionating column 2 by means of steam coil 3 oralternatively, not shown in the drawing, a conventional reboilersection. Fractionating column 2 is preferably operated at aboutatmospheric pressure, but may, although not a preferred method ofoperation, be operated at super-atmospheric or sub-atmosphericpressures. Cyclohexene from an external source entering through line 4,or recycled cyclohexene entering through line 5, is introduced throughline 6 into fractionating column '2 wherein it forms an azeotropewit'hthe water entering with the.

feed through line 1. This azeotrope, which boils at 70.8 C. at 760 mm.Hg abs. and contains about nine parts by weight of cyclohexene per partof water, is removed as overhead through line 7, condensed inwater-cooled condenser 8 and the condensate then passes down throughlines 9 and 1=1 int-o receiver 12 wherein the condensate collects andseparates into a lower aqueous layer 13 and an upper oily layer -1:4containing cylohexene. Non-condensible gases and vapors are releasedfrom the top of receiver 12 through line 1'5 and valve 16 and .may bedischarged to th-e atmosphere. The water from the phase separation,being virtually free from cyclohexene and other organic components, maybe discarded through line 117 to sewer. A portion of the condensateflowing down through line 9 may be returned to the Vtop of frac-Patented July 29, 1958v suliicient amount of cyclohexene is introducedfor a substantial length of time the cyclohexanone bottoms will containan increased concentration of water. The presence of water in thebottoms when subsequently fractionated in the second column to separatecyclohexanone from cyclohexanol will cause cyclohexanol to distill overand contaminate the cyclohexanone product due to the formation ofclose-boiling azeotropes of these substances with water. Conversely, ifsubstantially more cyclohexene is employed than is required to azeotropethe water, the excess will not be completely vaporized as overhead andwill tend to contaminate the cyclohexanone bottoms. This in turn willresult `in contamination of the distilled cyclohexanone product from thesecond column. Cyclohexene need be supplied usually in the initialstages of operation from an external source and introduced into thefractionating column through line 4 as shown in the drawing. Afterequilibrium conditions `are set up there will be sutiicient cyclohexenein layer 14 from which the cyclohexene may be removed through line '21and forced Iby pump 22 through lines 5 and 6 into tower 2. Any excesscyclohexene may be sent through line 23 to storage. The bottom of tower2 is maintained at a temperature of about 15S-165 C. by means of steamcoil 3 to provide heat for distilling the azeotrope and to volatilizethe water and other volatile constituents from thecyclohexanonecyclohexanol bottoms collecting in the bottom of tower 2.In this manner water can rbe completely removed in a single columninstead of requiring two columns as in the prior art. In addition, thisprovides a superior process due to simplification of procedure andequipment and reduction in amount of autocondensation Iby-productsformed due to shorter exposure of the cyclohexanone to elevatedtemperatures.

The dehydrated cyclohexene-free crude cyclohexanonecyclohexanol iscontinuously withdrawn from the bottom of column 2 through line 24 anddirected 'by pump 2S into fractionating column 26, similar inconstruction to column 2 except it is usually provided with a greaternurnber of bubble cap plates. Heat may be supplied to the `bottom oftower 6 (by means of a steam coil. Fractionating column 26 is operatedunder sub-atmospheric pressure of below about 100 mm. Hg abs.,preferably below about 50 mm. Hg abs. The temperature in column 26 willvary depending upon the pressure but generally will -be found to have atop temperature of about 70-90 C. and a bottom temperature of about to40 higher. Cyclohexanone vapors released from the top of column 26through line 27 are condensed in condenser 28 and then ow through line29 into receiver 31. A portion of the 'cyclohexanone condensatecollecting in receiver 31 is returned `by pump 32 through line 33 forreiiuxing and cooling into the top of tower 26. Vacuum is maintained onthe system through line 34 and valve 35 connected to the top of receiver31. High purity cyclohexanone collecting in receiver 31 is sent throughline 36 to storage. The cyclohexanol bottoms collecting in fractionatingcolumn 26 and heated 'by steam coil 37 are withdrawn and sent to storagethrough line 38.

The following example illustrates the present invention:

A stream of 3258 lbs./hr. of wet crude cyclohexanone, which was obtainedby dehydrogenation of cyclohexanol vapors over a zinc-copper catalystand which possessed the following analysis: 92.2% cyclohexanone, 5.3%

cyclohexanol, 1.4% cyclohexene, 0.5% water, 0.1% phenol and 0.5%condensation products-was fed into a 30 plate commercial bubble capcolumn at approximately the th plate. Sutiicient cyclohexene was fedinto the column at approximately the 15th plate to maintain the headtemperature at 70.5-71 C. at 760 mm. Hg abs. This quantity is normallyabout 101 lbs./hr. and must be suicient to give a total of 9 parts byweight of cyclohexene for each part of water in the feed. The columnoverhead with a rate of approximately 300 lbs./hr. was condensed in asuitable condenser, from which half of the condensate was returned tothe top of the column as reflux while the other hal-f was run to a phaseseparator, wherein it was automatically separated into a cyclohexenelayer and a water layer. A portion of the cyclohexene layer,approximately 101 lbs./hr., was recycled to the column, the remainderbeing drawn oi to storage. The water from the separator, equivalent toabout 16 lbs/hr. and containing less than 0.1% organic compounds, wasdiscarded to the sewer. Suicient heat was continuously fed to thereboiler located at the bottom of the column to maintain a temperatureof 160-l62 C. The bottoms, containing all of the cyclohexanone,cyclohexanol and higher boiling compounds of the feed and less than0.02% cyclohexene or water, were continuously withdrawn at a rate ofapproximately 3143 lbs./hr.

The bottoms from the dehydration column were fed continuously into a 60plate bubble cap column maintained at a head pressure of 50 mm. Hg abs.In this second column cyclohexanone was removed overhead at atemperature of 76 C. while a residue rich in cyclohexanol was withdrawnas bottoms. The cyclohexanone product thus obtained was found onanalysis to contain more than 99.95% cyclohexanone, less than 0.02% ofwater, cyclohexene or cyclohexanol and less than S0 p. p. rn. of phenol.

Although certain preferred embodiments of the invention have beendisclosed lfor purpose of illustration, it will be evident that variouschanges and modifications may be made therein without departing from thescope and spirit of the invention.

I claim:

l. A continuous process for separation and purification of cyclohexanonefrom cyclohexanone containing water and cyclohexanol as impurities whichcomprises continuously feeding a stream of impure cyclohexanone into afractionating zone, continuously introducing cyclohexene into saidfractionating zone to form an azeotrope with the water in said impurecyclohexanone, continuously removing as vapor lfrom the fractionatingzone the azeotrope composed of water and cyclohexene leaving dehydrated,cyclohexanone containing cyclohexanol as bottoms in the fractionatingzone, continuously condensing said vapor azeotrope, continuouslywithdrawing said dehydrated cyclohexanone containing cyclohexanol fromthe fractionating zone, passing said dehydratedcyclohexanche-cyclohexanol to a second fractionating zone maintained atan absolute pressure below about mm. Hg, continuously removingcyclohexanone vapor of high purity from said second fractionating zoneleaving cyclohexanol as bottoms in said second fractionating zone,continuously condensing and collecting said cyclohexanone of highpurity, and continuously withdrawing cyclohexanol as bottoms from thesecond fractionating zone.

2. A continuous process for separation and purification of cyclohexanonefrom cyclohexanone containing water and cyclohexanol as impurities whichcomprises continuously 4feeding a stream of impure cyclohexanone into afractionating zone, continuously introducing cyclohexene into saidfractionating zone to form an azeotrope with the water in said impurecyclohexanone, continuously removing as vapor from the fractionatingzone the azeotrope composed of water and cyclohexene leaving tionatingzone, continuously condensing and collecting said cyclohexanone of highpurity, and continuously withdrawing cyclohexanol as bottoms from thesecond fractionating zone.

3. A continuous process for separation and purication of cyclohexanonefrom cyclohexanone containing water, cyclohexanol and a minor amount ofcyclohexene which comprises continuously feeding a stream of impurecyclohexanone into a fractionating zone, continuously introducingcyclohexene into said fractionating zone to form an azeotrope with thewater in said impure cyclohexanone, continuously removing as vapor fromthe fraclil tionating zone the azeotrope composed of water andcyclohexene leaving `dehydrated Icyclohexanone containing cyclohexanolas bottoms in the fractionating zone, continuously condensing said vaporazeotrope, continuously separating said condensate into an aqueous phaseand an oil phase containing cyclohexene, continuously returningcyclohexene from the oil phase to the fractionating zone in an amountsuicient to maintain a proportion of about nine parts by weight ofcyclohexene per part of water in the fractionating zone, dischargingexcess oil phase containing cyclohexene from the system, continuouslyWithdrawing said dehydrated cyclohexanone containing cyclohexanol fromthe fractionating zone, passing said dehydratedcyclohexanone-cyclohexanol to a second fractionating zone maintained atan absolute pressure below about 100 mm. Hg, continuously removingcyclohexanone vapor of high purity from said second fractionating zoneleaving cyclohexanol as bottoms in said second fractionating zone,continuously condensing and collecting said cyclohexanone of highpurity, and continuously Withdrawing cyclohexanol as bottoms from thesecond fractionating zone.

y 4. A continuous process for separation and purication of cyclohexanonefrom cyclohexanone containing water and cyclohexanol as impurities whichcomprises continuously feeding a stream of impure cyclohexanone into afractionating zone maintained under substantial atmospheric pressure,contiriuously introducing cycloheXene into said fractionating zone toform an azeotrope with the water in said impure cyclohexanone,continuously removing as vapor from the fractionating zone the azeotropecomposed of water and cycloheXene leaving dehydrated cyclohexanonecontaining cyclohexanol as bottoms in the fractionating zone,continuously condensing said vapor azeotrope, returning a portion ofsaid condensate to the fractionating zone to maintain the temperature ofthe vapor leaving the fractionating zone at about 71 C., continuouslyseparating said condensate into an aqueous phase and an oil phasecontaining cyclohexene, continuously returning cyclohexene from the oilphase to the fractionating zone in an amount suflicient to maintain aproportion of about nine parts by weight of cyclohexene per part ofwater in the fractionating zone, continuously withdrawing saiddehydrated cyclohexanone containing cyclohexanol from the fractionatingzone, passing said dehydrated cycloheXanone-cyclohexanol to a secondfractionating zone maintained at an absolute pressure below about mm.Hg, continuously removing cyclohexanone vapor of high purity from saidsecond fractionating zone leaving cyclohexanol as bottoms in said secondfractionating zone, continuously condensing and collecting saidcyclohexanone of high purity, continuously returning a portion of said`condensate as reflux to said second fractionating zone, andcontinuously Withdrawing cyclohexanol as bottoms from the secondfractionating zone.

References Cited in the le of this patent UNITED STATES PATENTS FreyJune 5, 1945 Steitz May 15, 1951 OTHER REFERENCES Technique of OrganicChemistry, vol. 4; Distillation,

Weissberger, chapter 3, Interscience 1950.

1. A CONTINUOUS PROCESS FOR SEPARATION AND PURIFICATION OF CYCLOHEXANONEFROM CYCLOHEXANONE CONTAINING WATER AND CYCLOHEXANOL AS IMPURITIES WHICHCOMPRISES CONTINUOUSLY FEEDING A STREAM OF IMPURE CYCLOHEXANONE INTO AFRACTIONATING ZONE, CONTINUOUSLY INTRODUCING CYCLOHEXENE INTO SAIDFRACTIONATING ZONE TO FORM AN AZEOTROPE WITH THE WATER IN SAID IMPURECYCLOHEXANONE, CONTINUOUSLY REMOVING AS VAPOR FROM THE FRACTIONATINGZONE THE AZEOTROPE COMPOSED OF WATER AND CYCLOHEXENE LEAVING DEHYDRATEDCYCLOHEXANONE CONTAINING CYCLOHEXANOL AS BOTTOMS IN THE FRACTIONATINGZONE, CONTINUOUSLY CONDENSING SAID VAPOR AZEOTROPE, CONTINUOUSLYWITHDRAWING SAID DEHYDRATED CYCLOHEXANONE CONTAINING CYCLOHEXANOL FROMTHE FRACTIONATING ZONE, PASSING SAID DEHYDRATEDCYCLOHEXANONE-CYCLOHEXANOL TO A SECOND FRACTIONATING ZONE MAINTAINED ATAN ABSOLUTE PRESSURE BELOW ABOUT 100 MM. HG, CONTINUOUSLY REMOVINGCYCLOHEXANONE VAPOR OF HIGH PURITY FROM SAID SECOND FRACTIONATING ZONELEAVING CYCLOHEXANOL AS BOTTOMS IN SAID SECOND FRACTIONATING ZONE,CONTINUOUSLY CONDENSING AND COLLECTING SAID CYCLOHEXANONE OF HIGHPURITY, AND CONTINUOUSLY WITHDRAWING CYCLOHEXANOL AS BOTTOMS FROM THESECOND FRACTIONATING ZONE.